The invention further relates to an upset collar obtained by plastically deforming the material of the mentioned spindle of the inner ring of the wheel hub and having a particular geometry intended to obtain, on the upset collar and by means of a further plastic deformation, the mentioned frontal toothing, and to a wheel hub provided with a frontal toothing obtained with such a method and having improved mechanical performance.
In the wheel hubs of the aforesaid type, the frontal toothing has the purpose of coupling head-to-head the inner ring of the wheel hub and a corresponding frontal toothing of an outer ring of a constant velocity joint, to ensure the torque transmission from the constant velocity joint to the inner ring of the wheel hub, which carries a wheel of the vehicle by means of a flanged end thereof. A coupling of this type is described in U.S. Pat. No. 4,893,960, which also teaches how to make the frontal toothing on the inner ring of the wheel hub.
EP-B-1866553 teaches how to make the terminal portion of the spindle with a particular geometry which should facilitate the operation of obtaining, by means of plastic deformation, the upset collar, and especially avoid faults during the later step of forming the frontal toothing, which is obtained by means of the so-called “orbital forming” method directly onto the upset collar, indifferently either during or after the operation of forming the same, thus further obtaining, due to the particular geometry chosen for the terminal portion of the spindle, a final profile of the top or head or ridge of the teeth, observed in the radial direction, characterized by at least one discontinuity point between a first, radially outer segment thereof having a curved profile and a second rectilinear segment, which then connects to the base of the tooth by means of a third segment, also curved.
Although the above-described methods and configurations are relatively satisfactory, they lead to obtaining toothings which are not completely reliable in terms of wheel hub-constant velocity joint durability and which are subject to possible seizures when assembling the joint.
It is thus the object of the present invention to overcome the drawbacks of the prior art and in particular to provide a method of forming a frontal toothing on an inner ring of a wheel hub by means of plastic deformation, which is capable of ensuring improved performance in terms of working torque transmission, the dimensions being equal, high reliability in terms of durability of the joint consisting of the wheel hub-constant velocity joint, and smooth meshing without seizures between the toothing according to the invention and the corresponding complementary frontal toothing obtained on the outer ring of the constant velocity joint which, unlike that on the wheel hub, is obtained by casting/forging instead of by means of plastic deformation.